Microstructure and bending strength in the ternary (Mg,Ca)-partially-stabilized zirconia

This paper reports on microstructure and bending strength of commercial (MgO, CaO)-partially-stabilized zirconia subjected to heat treatments in the temperature range 900 degrees to 1550 degrees C. The as-received optimally aged material contained small ellipsoid-shaped tetragonal (t) precipitates dispersed homogeneously in the cubic (c) grains. Annealing at lower temperatures caused isothermal martensitic transformation to the monoclinic (m) phase. Annealing at higher temperatures caused formation of chevronlike and irregular-shaped cluster precipitates, due to stress-induced coarsening and precipitate impingement. The loss of bending strength was related to the stored strain energy contributed by each type of precipitate morphology, in addition to decrease in the volume fraction of the t phase